#include<bits/stdc++.h>

using namespace std;

double g(double x) {
    return x * x;
}

int main() {
    double x = 3;
    double (*f)(double);//����ָ��:����һ��double  xx(double)���ֺ���
    f = sqrt;
    cout << f(x) << endl;
    f = log;
    cout << f(x) << endl;
    f = sin;
    cout << f(x) << endl;
    f = g;
    cout << f(x) << endl;//9


}
